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Barium Hexaferrite Thin Films as a Scalable Magnetic-Insulator Platform for Proximity-Engineered Spintronics
Authors:
Shyam Sundar Poriah,
Sanjana D. S.,
Agrim Sharma,
Sreelakshmi M. Nair,
Pankaj Bhardwaj,
Laxmipriya Nanda,
Aryaman Das,
Jagadish Rajendran,
R. S. Patel,
Manish Jain,
Dhavala Suri
Abstract:
Rare-earth iron garnets, such as yttrium iron garnet (YIG) and thulium iron garnet (TmIG), are the benchmark magnetic insulators for spintronic and magnonic devices, but achieving usable perpendicular magnetic anisotropy (PMA) in these materials typically relies on substrate strain- engineering, requiring careful lattice-matching and specific growth conditions that constrain ma- terial accessibili…
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Rare-earth iron garnets, such as yttrium iron garnet (YIG) and thulium iron garnet (TmIG), are the benchmark magnetic insulators for spintronic and magnonic devices, but achieving usable perpendicular magnetic anisotropy (PMA) in these materials typically relies on substrate strain- engineering, requiring careful lattice-matching and specific growth conditions that constrain ma- terial accessibility. Here we establish sputter grown barium hexaferrite (BaFe12O19, BaM) as a magnetic-insulator alternative with strong intrinsic perpendicular anisotropy, requiring no strain engineering. X-ray diffraction, transmission electron microscopy and Raman spectroscopy confirm stoichiometric films with atomically smooth surfaces, while first-principles calculations corroborate a robust ferrimagnetic ground state. The films exhibit square out-of-plane hysteresis with a coercive field of nearly 0.1 T. Unlike rare-earth garnets, the perpendicular anisotropy in BaM is intrinsic to its magnetoplumbite crystal structure, arising independent of highly ordered strain. Interfaced with Pt and with exfoliated BiSbTeSe2 (BSTS), BaM induces proximity induced anomalous Hall trans- port, confirming efficient interfacial exchange coupling, while the BSTS/BaM heterostructure shows an additional Hall contribution suggestive of non-collinear interfacial spin textures. These results position BaM thin films as a scalable magnetic-insulator platform for spintronic and topological heterostructure devices beyond the constraints of garnet chemistry.
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Submitted 15 August, 2026;
originally announced August 2026.
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Anomalous Hall Effect in Silicon-Compatible Altermagnetic alpha-MnTe Thin Films
Authors:
Rajib Sarkar,
Subhransu Kumar Negi,
Arindom Das,
Arijit Mandal,
Pankaj Bhardwaj,
Sohini Guin,
Aryaman Das,
Naresh Shyaga,
Laxmipriya Nanda,
B. R. K. Nanda,
Dhavala Suri
Abstract:
Integrating spin-dependent functionality with mainstream semiconductor technology is a central goal of modern spintronics, yet most candidate materials remain incompatible with silicon-based platforms. Here, we report the direct epitaxial integration of alpha-MnTe thin films on Si(111) via molecular beam epitaxy and demonstrate a robust anomalous Hall effect (AHE) in this silicon-compatible alterm…
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Integrating spin-dependent functionality with mainstream semiconductor technology is a central goal of modern spintronics, yet most candidate materials remain incompatible with silicon-based platforms. Here, we report the direct epitaxial integration of alpha-MnTe thin films on Si(111) via molecular beam epitaxy and demonstrate a robust anomalous Hall effect (AHE) in this silicon-compatible altermagnetic system. Despite the absence of net magnetization, the films exhibit a pronounced hysteretic Hall response, providing clear evidence of finite Berry curvature generated by symmetry breaking in the thin-film geometry. High resolution structural and spectroscopic characterization confirms phase-pure, epitaxial growth with hexagonal NiAs-type symmetry, while magnetotransport measurements reveal correlated hysteresis in both transverse and longitudinal channels with systematic temperature evolution. First-principles calculations reveal substantial uncompensated Berry curvature arising from the spin-split band structure consistent with altermagnetic symmetry and the origin of the observed Hall response. These results establish MnTe/Si(111) as a silicon-compatible altermagnetic platform and chart a concrete pathway for embedding Berry-phase-driven functionalities into scalable semiconductor device architectures.
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Submitted 25 May, 2026;
originally announced May 2026.
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Vortex Transport in Ni/Bi Bilayer Superconductor with Strong Spin-Orbit and Exchange Interaction
Authors:
Laxmipriya Nanda,
Sohini Guin,
Yasen Hou,
Rajib Sarkar,
Naresh Shyaga,
Souvik Banerjee,
A. Sundaresan,
N. S. Vidhyadhiraja,
Jagadeesh S. Moodera,
Dhavala Suri
Abstract:
Nickel/bismuth (Ni/Bi) bilayers are a promising platform for exploring unconventional superconductivity. Ferromagnetic Ni is coupled to Bi, a strong spin orbit metal that only becomes superconducting below approx 10 mK, forming a bilayer exhibits superconductivity at a much higher temperatures, a Tc of 3 to 4 K. Such a bilayer thus makes an ideal system to probe Cooper pairing in strong spin orbit…
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Nickel/bismuth (Ni/Bi) bilayers are a promising platform for exploring unconventional superconductivity. Ferromagnetic Ni is coupled to Bi, a strong spin orbit metal that only becomes superconducting below approx 10 mK, forming a bilayer exhibits superconductivity at a much higher temperatures, a Tc of 3 to 4 K. Such a bilayer thus makes an ideal system to probe Cooper pairing in strong spin orbit coupled magnetic environments. Magneto transport studies near Tc reveal the behavior of vortex dynamics and exchange proximity effects. It is seen that isolated vortices of the bilayers respond sensitively to out of plane fields, producing antisymmetric transverse resistance peaks attributable to competing Magnus and viscous forces. Control experiments using a ferromagnetic insulator confirm that superconductivity extends throughout the bilayer, not just confined at the interface. Overall, the results provide a unified picture of transport dominated by vortex dynamics and show that a conventional s wave order parameter accounts for the observations, with any likely unconventional contributions being only subtle.
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Submitted 4 May, 2026;
originally announced May 2026.
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Crystallographic Orientation-Dependent Magnetotransport in the Layered Antiferromagnet -- CrSBr
Authors:
Naresh Shyaga,
Pankaj Bhardwaj,
Rajib Sarkar,
Jagadish Rajendran,
Abhiram Soori,
Dhavala Suri
Abstract:
Among two-dimensional magnetic materials, CrSBr has attracted considerable attention owing to its coexistence of ferromagnetic and antiferromagnetic ordering, which depends sensitively on crystallographic orientation. An additional distinguishing feature of CrSBr is its highly anisotropic Fermi surface in momentum space. In this work, we present a comprehensive investigation of magnetoresistance b…
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Among two-dimensional magnetic materials, CrSBr has attracted considerable attention owing to its coexistence of ferromagnetic and antiferromagnetic ordering, which depends sensitively on crystallographic orientation. An additional distinguishing feature of CrSBr is its highly anisotropic Fermi surface in momentum space. In this work, we present a comprehensive investigation of magnetoresistance by systematically orienting the bias current and the applied magnetic field along all three crystallographic axes. We demonstrate that the magnetoresistance serves as a direct probe of electronic anisotropy, exhibiting pronounced variations when the current is applied along different crystallographic directions under a magnetic field perpendicular to the sample plane. For in-plane magnetic fields, we observe conventional anisotropic magnetoresistance accompanied by hysteresis, indicative of ferromagnetic behavior. Overall, our study provides a complete picture of electronic transport in CrSBr as a function of bias current and magnetic field orientation with respect to crystallographic directions, thereby opening pathways for future experiments requiring high sensitivity of electrical resistance to magnetic field gradients.
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Submitted 23 March, 2026;
originally announced March 2026.
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Nitrogen-Vacancy-Mediated Magnetism in Sputtered GdN Thin Films
Authors:
Pankaj Bhardwaj,
Jyotirmoy Sarkar,
Bubun Biswal,
Subhransu Kumar Negi,
Arijit Sinha,
Anirudh Venugopalrao,
Sharath Kumar C,
Sreelakshmi M Nair,
R. S. Patel,
Deepshika Jaiswal Nagar,
Abhishek Mishra,
Srinivasan Raghavan,
Umesh Waghmare,
Dhavala Suri
Abstract:
Among rare-earth nitrides (RENs), gadolinium nitride (GdN) stands out as a promising material for spintronics owing to its distinctive combination of semiconducting behavior, strong exchange interactions, and intrinsically soft ferromagnetism. Its relatively high Curie temperature and large saturation magnetization make it an attractive candidate for device concepts such as non-volatile memory ele…
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Among rare-earth nitrides (RENs), gadolinium nitride (GdN) stands out as a promising material for spintronics owing to its distinctive combination of semiconducting behavior, strong exchange interactions, and intrinsically soft ferromagnetism. Its relatively high Curie temperature and large saturation magnetization make it an attractive candidate for device concepts such as non-volatile memory elements and spin-based transistors, motivating efforts toward low-cost, uniform, and compositionally controlled thin-film growth. In this work, we deposited GdN thin films on SiO2/AlN substrates using DC sputtering under reactive nitridation conditions, with thicknesses varying from 18 to 180 nm, and systematically investigated their structural and magnetic properties. The films exhibit soft ferromagnetic ordering, characterized by a coercive field of approximately 200 Oe and a Curie temperature (Tc) near 70 K. Structural analysis reveals lattice distortions and local strain associated with nitrogen-vacancy defects, whose concentration varies with film thickness. Our theoretical studies establish a direct correlation between the observed Raman modes of the GdN lattice and the reduced magnetization induced by nitrogen vacancies. These vacancies give rise to defect-mediated ferromagnetism, leading to a measurable enhancement of Tc from 68 K to 82 K across the studied thickness range. The observed magnetic behavior is well described by the bound magnetic polaron (BMP) model, confirming that nitrogen vacancies are key contributors to ferromagnetic ordering while preserving the soft-magnetic character intrinsic to GdN. This study underscores the pivotal role of defect engineering in optimizing GdN thin films for spintronics applications.
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Submitted 14 March, 2026;
originally announced March 2026.
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Magneto-Chiral Anisotropy in Josephson Diode Effect of All-Metallic Lateral Junctions with Interfacial Rashba Spin-Orbit Coupling
Authors:
Maximilian Mangold,
Lorenz Bauriedl,
Johanna Berger,
Chang Yu-Cheng,
Thomas N. G. Meier,
Matthias Kronseder,
Pertti Hakonen,
Christian H. Back,
Christoph Strunk,
Dhavala Suri
Abstract:
We explore the role of interfacial Rashba spin-orbit coupling (SOC) for the Josephson diode effect in all-metal diffusive Josephson junctions. Devices with Fe/Pt and Cu/Pt weak links between Nb leads reveal a Josephson diode effect in an in-plane magnetic field with magneto-chiral anisotropy according to the point symmetry of Rashba SOC. The Rashba SOC originates from inversion symmetry breaking a…
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We explore the role of interfacial Rashba spin-orbit coupling (SOC) for the Josephson diode effect in all-metal diffusive Josephson junctions. Devices with Fe/Pt and Cu/Pt weak links between Nb leads reveal a Josephson diode effect in an in-plane magnetic field with magneto-chiral anisotropy according to the point symmetry of Rashba SOC. The Rashba SOC originates from inversion symmetry breaking at the metal-metal interfaces. A control sample with a plain Cu-layer as weak link, in contrast, exhibits an axis-symmetric diode effect. The Fraunhofer patterns display an apparent inverted hysteresis which can be traced back to stray fields resulting from the conventional hysteretic vortex pinning in the Nb contacts.
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Submitted 27 April, 2026; v1 submitted 2 November, 2025;
originally announced November 2025.
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Time Reversal Symmetry Broken Electronic Phases in Thin Films of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$
Authors:
Sohini Guin,
Naresh Shyaga,
Jagadish Rajendran,
Aryaman Das,
Subhransu Kumar Negi,
Saisab Bhowmik,
Pankaj Bhardwaj,
U. Chandni,
Dhavala Suri
Abstract:
High-temperature superconductors (high-Tc SCs) host a rich landscape of electronic phases encompassing the pseudogap, strange metal, superconducting, antiferromagnetic insulating, and Fermi-liquid regimes. The superconducting phase is notable for non-dissipative electronic functionality at relatively high temperatures. These phases are commonly probed in thermodynamic phase space by varying temper…
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High-temperature superconductors (high-Tc SCs) host a rich landscape of electronic phases encompassing the pseudogap, strange metal, superconducting, antiferromagnetic insulating, and Fermi-liquid regimes. The superconducting phase is notable for non-dissipative electronic functionality at relatively high temperatures. These phases are commonly probed in thermodynamic phase space by varying temperature or current through the sample. They can also be probed by breaking time-reversal symmetry (TRS) with an external magnetic field, which yields transition signatures distinct from those arising solely from temperature or current tuning. Here we show that electron transport in Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ is primarily governed by two-dimensional superconductivity consistent with a Berezinskii-Kosterlitz-Thouless (BKT) topological phase transition, as supported by current-voltage characteristics measured under temperature variation; these measurements preserve TRS. In contrast, when an external magnetic field is applied, the superconducting state is consistently preceded by weak antilocalization (WAL), where bound vortex-antivortex pairs dissociate into a normal metallic state through an intermediate localized phase. We further establish that highly disordered films exhibit transport dominated by three-dimensional weak localization, with superconductivity entirely suppressed.
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Submitted 12 August, 2026; v1 submitted 2 November, 2025;
originally announced November 2025.
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Tracing Dirac points of topological surface states by ferromagnetic resonance
Authors:
Laura Pietanesi,
Magdalena Marganska,
Thomas Mayer,
Michael Barth,
Lin Chen,
Ji Zou,
Adrian Weindl,
Alexander Liebig,
Rebeca Díaz-Pardo,
Dhavala Suri,
Florian Schmid,
Franz J. Gießibl,
Klaus Richter,
Yaroslav Tserkovnyak,
Matthias Kronseder,
Christian H. Back
Abstract:
Ferromagnetic resonance is used to reveal features of the buried electronic band structure at interfaces between ferromagnetic metals and topological insulators. By monitoring the evolution of magnetic damping, the application of this method to a hybrid structure consisting of a ferromagnetic layer and a 3D topological insulator reveals a clear fingerprint of the Dirac point and exhibits additiona…
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Ferromagnetic resonance is used to reveal features of the buried electronic band structure at interfaces between ferromagnetic metals and topological insulators. By monitoring the evolution of magnetic damping, the application of this method to a hybrid structure consisting of a ferromagnetic layer and a 3D topological insulator reveals a clear fingerprint of the Dirac point and exhibits additional features of the interfacial band structure not otherwise observable. The underlying spin-pumping mechanism is discussed in the framework of dissipation of angular momentum by topological surface states (TSSs). Tuning of the Fermi level within the TSS was verified both by varying the stoichiometry of the topological insulator layer and by electrostatic backgating and the damping values obtained in both cases show a remarkable agreement. The high energy resolution of this method additionally allows us to resolve the energetic shift of the local Dirac points generated by local variations of the electrostatic potential. Calculations based on the chiral tunneling process naturally occurring in TSS agree well with the experimental results.
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Submitted 7 March, 2024; v1 submitted 6 March, 2024;
originally announced March 2024.
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Enhanced Ferromagnetism in Monolayer Cr2Te3 via Topological Insulator Coupling
Authors:
Yunbo Ou,
Murod Mirzhalilov,
Norbert M. Nemes,
Jose L. Martinez,
Mirko Rocci,
Alexander Duong,
Austin Akey,
Alexandre C. Foucher,
Wenbo Ge,
Dhavala Suri,
Yiping Wang,
Haile Ambaye,
Jong Keum,
Mohit Randeria,
Nandini Trivedi,
Kenneth S. Burch,
David C. Bell,
Frances M. Ross,
Weida Wu,
Don Heiman,
Valeria Lauter,
Jagadeesh S. Moodera,
Hang Chi
Abstract:
Exchange-coupled interfaces are pivotal in exploiting two-dimensional (2D) ferromagnetism. Due to the extraordinary correlations among charge, spin, orbital and lattice degrees of freedom, layered magnetic transition metal chalcogenides (TMCs) bode well for exotic topological phenomena. Here we report the realization of wafer-scale Cr2Te3 down to monolayer (ML) on insulating SrTiO3(111) and/or Al2…
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Exchange-coupled interfaces are pivotal in exploiting two-dimensional (2D) ferromagnetism. Due to the extraordinary correlations among charge, spin, orbital and lattice degrees of freedom, layered magnetic transition metal chalcogenides (TMCs) bode well for exotic topological phenomena. Here we report the realization of wafer-scale Cr2Te3 down to monolayer (ML) on insulating SrTiO3(111) and/or Al2O3(001) substrates using molecular beam epitaxy. Robust ferromagnetism persists in the 2D limit. In particular, the Curie temperature TC of 2 ML Cr2Te3 increases from 100 K to ~ 120 K when proximitized to topological insulator (TI) (Bi,Sb)2Te3, with substantially boosted magnetization as observed via polarized neutron reflectometry. Our experiments and theory strongly indicate that the Bloembergen-Rowland interaction is likely universal underlying TC enhancement in TI-coupled magnetic heterostructures. The topological-surface-enhanced magnetism in 2D TMC enables further exchange coupling physics and quantum hybrid studies, including paving the way to realize interface-modulated topological electronics.
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Submitted 15 May, 2025; v1 submitted 22 December, 2023;
originally announced December 2023.
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Transport across junctions of altermagnets with normal metals and ferromagnets
Authors:
Sachchidanand Das,
Dhavala Suri,
Abhiram Soori
Abstract:
Altermagnet (AM) is a novel time reversal symmetry broken magnetic phase with $d$-wave order which has been experimentally realized recently. We discuss theoretical models of altermagnet based systems on lattice and in continuum. We show equivalence between the lattice and continuum models by mapping the respective parameters. We study (i) altermagnet-normal metal (NM) and (ii) altermagnet-ferroma…
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Altermagnet (AM) is a novel time reversal symmetry broken magnetic phase with $d$-wave order which has been experimentally realized recently. We discuss theoretical models of altermagnet based systems on lattice and in continuum. We show equivalence between the lattice and continuum models by mapping the respective parameters. We study (i) altermagnet-normal metal (NM) and (ii) altermagnet-ferromagnet (FM) junctions, with the aim to quantify transport properties such as conductivity and magnetoresistance. We find that a spin current accompanies charge current when a bias is applied. The magnetoresistance of AM-FM junction switches sign when AM is rotated by $90^{\circ}$ -- a feature unique to the altermagnetic phase.
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Submitted 27 July, 2023; v1 submitted 11 May, 2023;
originally announced May 2023.
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Non-reciprocity of Vortex-limited Critical Current in Conventional Superconducting Micro-bridges
Authors:
Dhavala Suri,
Akashdeep Kamra,
Thomas N. G. Meier,
Matthias Kronseder,
Wolfgang Belzing,
Christian H. Back,
Christoph Strunk
Abstract:
Non-reciprocity in the critical current has been observed in a variety of superconducting systems and has been called the superconducting diode effect. The origin underlying the effect depends on the symmetry breaking mechanisms at play. We investigate superconducting micro bridges of NbN and also NbN/magnetic insulator (MI) hybrids. We observe a large diode efficiency of $\approx$~30\% when an ou…
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Non-reciprocity in the critical current has been observed in a variety of superconducting systems and has been called the superconducting diode effect. The origin underlying the effect depends on the symmetry breaking mechanisms at play. We investigate superconducting micro bridges of NbN and also NbN/magnetic insulator (MI) hybrids. We observe a large diode efficiency of $\approx$~30\% when an out-of-plane magnetic field as small as 25~mT is applied. In both NbN and NbN/MI hybrid, we find that the diode effect vanishes when the magnetic field is parallel to the sample plane. Our observations are consistent with the critical current being determined by the vortex surface barrier. Unequal barriers on the two edges of the superconductor strip result in the diode effect. Furthermore, the rectification is observed up to a temperature $\sim$10~K, which makes the device potential for diode based applications over larger temperature range than before.
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Submitted 13 September, 2022;
originally announced September 2022.
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Interfacial control of vortex-limited critical current in type II superconductor films
Authors:
Marius K. Hope,
Morten Amundsen,
Dhavala Suri,
Jagadeesh S. Moodera,
Akashdeep Kamra
Abstract:
In a small subset of type II superconductor films, the critical current is determined by a weakened Bean-Livingston barrier posed by the film surfaces to vortex penetration into the sample. A film property thus depends sensitively on the surface or interface to an adjacent material. We theoretically investigate the dependence of vortex barrier and critical current in such films on the Rashba spin-…
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In a small subset of type II superconductor films, the critical current is determined by a weakened Bean-Livingston barrier posed by the film surfaces to vortex penetration into the sample. A film property thus depends sensitively on the surface or interface to an adjacent material. We theoretically investigate the dependence of vortex barrier and critical current in such films on the Rashba spin-orbit coupling at their interfaces with adjacent materials. Considering an interface with a magnetic insulator, we find the spontaneous supercurrent resulting from the exchange field and interfacial spin-orbit coupling to substantially modify the vortex surface barrier, consistent with a previous prediction. Thus, we show that the critical currents in superconductor-magnet heterostructures can be controlled, and even enhanced, via the interfacial spin-orbit coupling. Since the latter can be controlled via a gate voltage, our analysis predicts a class of heterostructures amenable to gate-voltage modulation of superconducting critical currents. It also sheds light on the recently observed gate-voltage enhancement of critical current in NbN superconducting films.
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Submitted 18 November, 2021; v1 submitted 9 August, 2021;
originally announced August 2021.
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Emergence of Unconventional Interfacial Magnetic Phenomenon in Topological Insulator-Based Magnetic Heterostructures
Authors:
Dhavala Suri,
Archit Bhardwaj,
Satyaki Sasmal,
Karthik Raman
Abstract:
In a topological insulator (TI)/magnetic insulator (MI) hetero-structure, large spin-orbit coupling of the TI and inversion symmetry breaking at the interface could foster non-planar spin textures such as skyrmions at the interface. This is observed as topological Hall effect in a conventional Hall set-up. While this effect has been observed at the interface of TI/MI, where MI beholds perpendicula…
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In a topological insulator (TI)/magnetic insulator (MI) hetero-structure, large spin-orbit coupling of the TI and inversion symmetry breaking at the interface could foster non-planar spin textures such as skyrmions at the interface. This is observed as topological Hall effect in a conventional Hall set-up. While this effect has been observed at the interface of TI/MI, where MI beholds perpendicular magnetic anisotropy, non-trivial spin-textures that develop in interfacial MI with in-plane magnetic anisotropy is under-reported. In this work, we study Bi$_2$Te$_3$/EuS hetero-structure using planar Hall effect (PHE). We observe planar topological Hall and spontaneous planar Hall features that are characteristic of non-trivial in-plane spin textures at the interface. We find that the latter is minimum when the current and magnetic field directions are aligned parallel, and maximum when they are aligned perpendicularly within the sample plane, which maybe attributed to the underlying planar anisotropy of the spin-texture. These results demonstrate the importance of PHE for sensitive detection and characterization of non-trivial magnetic phase that has evaded exploration in the TI/MI interface.
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Submitted 23 September, 2021; v1 submitted 8 July, 2021;
originally announced July 2021.
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In-depth Analysis of Anisotropic Magnetoconductance in Bi$_2$Se$_3$ thin films with electron-electron interaction corrections
Authors:
Satyaki Sasmal,
Joynarayan Mukherjee,
Dhavala Suri,
Karthik V. Raman
Abstract:
A combination of out-of-plane and in-plane magnetoconductance (MC) study in topological insulators (TI) is often used as an experimental technique to probe weak anti-localization (WAL) response of the topological surface states (TSSs). However, in addition to the above WAL response, weak localization (WL) contribution from conducting bulk states are also known to coexist and contribute to the over…
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A combination of out-of-plane and in-plane magnetoconductance (MC) study in topological insulators (TI) is often used as an experimental technique to probe weak anti-localization (WAL) response of the topological surface states (TSSs). However, in addition to the above WAL response, weak localization (WL) contribution from conducting bulk states are also known to coexist and contribute to the overall MC; a study that has so far received limited attention. In this article, we accurately extract the above WL contribution by systematically analyzing the temperature and magnetic field dependency of conductivity in Bi$_2$Se$_3$ films. For accurate analysis, we quantify the contribution of electron-electron interactions to the measured MC which is often ignored in recent WAL studies. Moreover, we show that the WAL effect arising from the TSSs with finite penetration depth, for out-of-plane and in-plane magnetic field can together explain the anisotropic magnetoconductance (AMC) and, thus, the investigated AMC study can serve as a useful technique to probe the parameters like phase coherence length and penetration depth that characterise the TSSs in 3D TIs. We also demonstrate that increase in bulk-disorder, achieved by growing the films on amorphous SiO$_2$ substrate rather than on crystalline Al$_2$O$_3$(0001), can lead to stronger decoupling between the top and bottom surface states of the film.
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Submitted 17 June, 2021; v1 submitted 14 June, 2021;
originally announced June 2021.
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Observation of Planar Hall Effect in Topological Insulator -- Bi$_2$Te$_3$
Authors:
Archit Bhardwaj,
Syam Prasad P.,
Karthik Raman,
Dhavala Suri
Abstract:
Planar Hall effect (PHE) in topological insulators (TIs) is discussed as an effect that stems mostly from conduction due to topologically protected surface states. Although surfaces states play a critical role and are of utmost importance in TIs, our present study reflects the need for considering the bulk conduction in understanding PHE in TIs. Here, we demonstrate an enhancement in PHE amplitude…
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Planar Hall effect (PHE) in topological insulators (TIs) is discussed as an effect that stems mostly from conduction due to topologically protected surface states. Although surfaces states play a critical role and are of utmost importance in TIs, our present study reflects the need for considering the bulk conduction in understanding PHE in TIs. Here, we demonstrate an enhancement in PHE amplitude by three times by doubling the thickness of Bi$_2$Te$_3$ film on Si (111). The PHE amplitude reaches $\approx$~6 n$Ω$m in 30 quintuple layer (QL) device as compared to $\approx$~2 n$Ω$m in 14 QL. We find that the PHE amplitude increases with temperature in the 30 QL Bi$_2$Te$_3$ films grown on Si (111) and Al$_2$O$_3$ (0001). Our experiments indicate that the contribution of bulk states to PHE in TIs could be significant.
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Submitted 1 June, 2021; v1 submitted 12 April, 2021;
originally announced April 2021.
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Finite transverse conductance in topological insulators under an applied in-plane magnetic field
Authors:
Dhavala Suri,
Abhiram Soori
Abstract:
Recently, in topological insulators (TIs) the phenomenon of planar Hall effect (PHE) wherein a current driven in presence an in-plane magnetic field generates a transverse voltage has been experimentally witnessed. There have been a couple of theoretical explanations of this phenomenon. We investigate this phenomenon based on scattering theory on a normal metal-TI-normal metal hybrid structure and…
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Recently, in topological insulators (TIs) the phenomenon of planar Hall effect (PHE) wherein a current driven in presence an in-plane magnetic field generates a transverse voltage has been experimentally witnessed. There have been a couple of theoretical explanations of this phenomenon. We investigate this phenomenon based on scattering theory on a normal metal-TI-normal metal hybrid structure and calculate the conductances in longitudinal and transverse directions to the applied bias. The transverse conductance depends on the spatial location between the two NM-TI junctions where it is calculated. It is zero in the drain electrode when the chemical potentials of the top and the bottom TI surfaces ($μ_t$ and $μ_b$ respectively) are equal. The longitudinal conductance is $π$-periodic in $φ$-the angle between the bias direction and the direction of the in-plane magnetic field. The transverse conductance is $π$-periodic in $φ$ when $μ_t=μ_b$ whereas it is $2π$-periodic in $φ$ when $μ_t\neqμ_b$. As a function of the magnetic field, the magnitude of transverse conductance increases initially and peaks. At higher magnetic fields, it decays for angles $φ$ closer to $0,π$ whereas oscillates for angles $φ$ close to $π/2$. The conductances oscillate with the length of the TI region. A finite width of the system makes the transport separate into finitely many channels. The features of the conductances are similar to those in the limit of infinitely wide system except when the width is so small that only one channel participates in the transport. When only one channel participates in transport, the transverse conductance in the region $0<x<L$ is zero for $μ_t=μ_b$ and the transverse conductance in the region $x>L$ is zero even for the case $μ_t\neqμ_b$. We understand the features in the obtained results.
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Submitted 29 April, 2021; v1 submitted 19 January, 2021;
originally announced January 2021.
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Modulation Doping via a 2d Atomic Crystalline Acceptor
Authors:
Yiping Wang,
Jesse Balgley,
Eli Gerber,
Mason Gray,
Narendra Kumar,
Xiaobo Lu,
Jia-Qiang Yan,
Arash Fereidouni,
Rabindra Basnet,
Seok Joon Yun,
Dhavala Suri,
Hikari Kitadai,
Takashi Taniguchi,
Kenji Watanabe,
Xi Ling,
Jagadeesh Moodera,
Young Hee Lee,
Hugh O. H. Churchill,
Jin Hu,
Li Yang,
Eun-Ah Kim,
David G. Mandrus,
Erik A. Henriksen,
Kenneth S. Burch
Abstract:
Two-dimensional (2d) nano-electronics, plasmonics, and emergent phases require clean and local charge control, calling for layered, crystalline acceptors or donors. Our Raman, photovoltage, and electrical conductance measurements combined with \textit{ab initio} calculations establish the large work function and narrow bands of $α$-RuCl$_3$ enable modulation doping of exfoliated, chemical vapor de…
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Two-dimensional (2d) nano-electronics, plasmonics, and emergent phases require clean and local charge control, calling for layered, crystalline acceptors or donors. Our Raman, photovoltage, and electrical conductance measurements combined with \textit{ab initio} calculations establish the large work function and narrow bands of $α$-RuCl$_3$ enable modulation doping of exfoliated, chemical vapor deposition (CVD), and molecular beam epitaxy (MBE) materials. Short-ranged lateral doping (${\leq}65\ \text{nm}$) and high homogeneity are achieved in proximate materials with a single layer of \arucl. This leads to the highest monolayer graphene (mlg) mobilities ($4,900\ \text{cm}^2/ \text{Vs}$) at these high hole densities ($3\times10^{13}\ \text{cm}^{-2}$); and yields larger charge transfer to bilayer graphene (blg) ($6\times10^{13}\ \text{cm}^{-2}$). We further demonstrate proof of principle optical sensing, control via twist angle, and charge transfer through hexagonal boron nitride (hBN).
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Submitted 15 July, 2020; v1 submitted 13 July, 2020;
originally announced July 2020.
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Strain-Tuned Magnetic Anisotropy in Sputtered Thulium Iron Garnet Ultrathin Films and TIG/Au/TIG Valve Structures
Authors:
Gilvânia Vilela,
Hang Chi,
Gregory Stephen,
Charles Settens,
Preston Zhou,
Yunbo Ou,
Dhavala Suri,
Don Heiman,
Jagadeesh Moodera
Abstract:
Defining the magnetic anisotropy for in-plane or out-of-plane easy axis in ferrimagnetic insulators films by controlling the strain, while maintaining high-quality surfaces, is desirable for spintronic and magnonic applications. We investigate ways to tune the anisotropy of amorphous sputtered ultrathin thulium iron garnet (TIG) films, and thus tailor their magnetic properties by the thickness (7.…
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Defining the magnetic anisotropy for in-plane or out-of-plane easy axis in ferrimagnetic insulators films by controlling the strain, while maintaining high-quality surfaces, is desirable for spintronic and magnonic applications. We investigate ways to tune the anisotropy of amorphous sputtered ultrathin thulium iron garnet (TIG) films, and thus tailor their magnetic properties by the thickness (7.5 to 60 nm), substrate choice (GGG and SGGG), and crystallization process. We correlate morphological and structural properties with the magnetic anisotropy of post-growth annealed films. 30 nm thick films annealed at 600 °C show compressive strain favoring an in-plane magnetic anisotropy (IPMA), whereas films annealed above 800 °C are under a tensile strain leading to a perpendicular magnetic anisotropy (PMA). Air-annealed films present a high degree of crystallinity and magnetization saturation close to the bulk value. These results lead to successful fabrication of trilayers TIG/Au/TIG, with coupling between the TIG layers depending on Au thickness. These results will facilitate the use of TIG to create various in situ clean hybrid structures for fundamental interface exchange studies, and towards the development of complex devices. Moreover, the sputtering technique is advantageous as it can be easily scaled up for industrial applications.
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Submitted 21 September, 2020; v1 submitted 24 February, 2020;
originally announced February 2020.
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Resistivity Anomaly in Weyl Semimetal candidate Molybdenum Telluride
Authors:
Dhavala Suri,
Christopher Linderalv,
Bogdan Karpiak,
Linnea Anderson,
Sandeep Kumar Singh,
Andre Dankert,
F. C. Chou,
Raman Sankar,
F. C. Chou,
Paul Erhart,
Saroj P. Dash,
R. S. Patel
Abstract:
The Weyl semi-metal candidate MoTe$_{2}$ is expected to exhibit a range of exotic electronic transport properties. It exhibits a structural phase transition near room temperature that is evident in the thermal hysteresis in resistivity and thermopower (Seebeck coefficient) as well as large spin-orbit interaction. Here, we also document a resistivity anomaly of up to 13% in the temperature window b…
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The Weyl semi-metal candidate MoTe$_{2}$ is expected to exhibit a range of exotic electronic transport properties. It exhibits a structural phase transition near room temperature that is evident in the thermal hysteresis in resistivity and thermopower (Seebeck coefficient) as well as large spin-orbit interaction. Here, we also document a resistivity anomaly of up to 13% in the temperature window between 25 and 50 K, which is found to be strongly anisotropic. Based on the experimental data in conjunction with density functional theory calculations, we conjecture that the anomaly can be related to the presence of defects in the system. These findings open opportunities for further investigations and understanding of the transport behavior in these newly discovered semi-metallic layered systems.
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Submitted 16 January, 2018;
originally announced January 2018.
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A study of electron and thermal transport in layered Titanium disulphide single crystals
Authors:
Dhavala Suri,
Vantari Siva,
Shalikram Joshi,
Kartik Senapati,
P. K. Sahoo,
Shikha Varma,
R. S. Patel
Abstract:
We present a detailed study of thermal and electrical transport behavior of single crystal Titanium disulphide flakes, which belongs to the two dimensional, transition metal dichalcogenide class of materials. In-plane Seebeck effect measurements revealed a typical metal-like linear temperature dependence in the range of 85 - 285 K. Electrical transport measurements with in-plane current geometry e…
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We present a detailed study of thermal and electrical transport behavior of single crystal Titanium disulphide flakes, which belongs to the two dimensional, transition metal dichalcogenide class of materials. In-plane Seebeck effect measurements revealed a typical metal-like linear temperature dependence in the range of 85 - 285 K. Electrical transport measurements with in-plane current geometry exhibited a nearly T^2 dependence of resistivity in the range of 10 - 300 K. However, transport measurements along the out-of-plane current geometry showed a transition in temperature dependence of resistivity from T^2 to T^5 beyond 200 K. Interestingly, Au ion-irradiated TiS2 samples showed a similar T 5 dependence of resistivity beyond 200 K, even in the current-in-plane geometry. Micro- Raman measurements were performed to study the phonon modes in both pristine and ion-irradiated TiS2 crystals.
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Submitted 15 January, 2018;
originally announced January 2018.
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Electron transport in magnetic tunnel junctions -- a theoretical study of lattice and continuum models
Authors:
Dhavala Suri,
R. S. Patel,
Abhiram Soori
Abstract:
Magnetic tunnel junctions comprising of an insulator sandwiched between two ferromagnetic films are the simplest spintronic devices. Theoretically, these can be modeled by a metallic Hamiltonian in both the lattice and the continuum with an addition of Zeeman field. We calculate conductance at arbitrary orientations of the easy axes of the two ferromagnets. When mapped, the lattice and the continu…
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Magnetic tunnel junctions comprising of an insulator sandwiched between two ferromagnetic films are the simplest spintronic devices. Theoretically, these can be modeled by a metallic Hamiltonian in both the lattice and the continuum with an addition of Zeeman field. We calculate conductance at arbitrary orientations of the easy axes of the two ferromagnets. When mapped, the lattice and the continuum models show a discrepancy in conductance in the limit of a large Zeeman field. We resolve the discrepancy by modeling the continuum theory in an appropriate way.
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Submitted 29 August, 2019; v1 submitted 10 August, 2017;
originally announced August 2017.
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Electron and thermal transport via Variable Range Hopping in MoSe$_{2}$ single crystals
Authors:
Dhavala Suri,
R. S. Patel
Abstract:
Bulk single crystal Molybdenum diselenide has been studied for its electronic and thermal transport properties. We perform resistivity measurements with current in-plane (CIP) and current perpendicular to plane (CPP) as a function of temperature. The CIP measurements exhibit metal to semiconductor transition at $\simeq 31$ K. In the semiconducting phase ($T > 31$ K), the transport is best explaine…
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Bulk single crystal Molybdenum diselenide has been studied for its electronic and thermal transport properties. We perform resistivity measurements with current in-plane (CIP) and current perpendicular to plane (CPP) as a function of temperature. The CIP measurements exhibit metal to semiconductor transition at $\simeq 31$ K. In the semiconducting phase ($T > 31$ K), the transport is best explained by variable range hopping (VRH) model. Large magnitude of resistivity in CPP mode indicates strong structural anisotropy. Seebeck coefficient as a function of temperature measured in the range $90 - 300$ K, also agrees well with the VRH model. The room temperature Seebeck coefficient is found to be $139$ $μ$V/K. VRH fittings of the resistivity and Seebeck coefficient data indicate high degree of localization.
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Submitted 8 July, 2017;
originally announced July 2017.
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Spin Hall Effect measurement techniques
Authors:
Dhavala Suri,
R. S. Patel
Abstract:
Spin Hall Effect is relativistic quantum mechanical effect which enables non-magnetic materials show magnetic phenomena without the application of a magnetic field. With spin Hall Effect, one can realize spintronics devices operating purely on electrical and optical means and eliminate the use of ferromagnets which have associated fringe fields. In this review article, we present the experimental…
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Spin Hall Effect is relativistic quantum mechanical effect which enables non-magnetic materials show magnetic phenomena without the application of a magnetic field. With spin Hall Effect, one can realize spintronics devices operating purely on electrical and optical means and eliminate the use of ferromagnets which have associated fringe fields. In this review article, we present the experimental developments and current understanding of the Spin Hall Effect Phenomena. We discuss various experiments as well as device structures which employ electrical, optical or both techniques to demonstrate Spin Hall effect. Most of these devices structures are simple and easy to fabricate in modern laboratories.
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Submitted 10 August, 2017; v1 submitted 18 June, 2015;
originally announced June 2015.